1. Field of the Invention
The invention relates to a lock device with a lock cylinder and a flat key having a control gate.
2. Description of the Background Art
Conventional lock devices are known from the prior art. High demands are placed on such lock devices with regard to security against break-in, so that simple reading out of the unlocking positions of the different tumblers should be prevented. A tumbler typically has locking edges on both sides that project into a specific locking channel of the cylinder housing in the locking position. In this design, the locking edges are designed such that they are flush with the cylinder core or its outer circumferential edge in at least one position of the tumbler so that in this position they permit the cylinder core to rotate. This position is hence also referred to as the unlocking position of the tumbler. Without special precautions, the unlocking position of the tumblers can be probed, for example directly in the keyway from the rest positions of the tumblers with the flat key removed, or indirectly by determining the length of the applicable return travel of each tumbler when the individual tumblers are successively pushed back in opposition to their spring loading using a tool. Using the data thus obtained, an unauthorized person can then ascertain the control gate required for unlocking and produce a matching duplicate key.
To increase security, it is known to provide such lock devices with read-out protection that conceals the unlocking position of the tumblers. For example, an advantageous read-out protection is disclosed in DE 103 13 125 A1, which corresponds to U.S. Pat. No. 2007006623. Here, provision is made to equip the tumblers with at least one stop that restricts the displacement travel of the relevant tumbler in the cylinder core in at least one of the two directions of displacement. This achieves the result that, when the key is removed, the relevant tumbler is pushed or moved to the stop by spring loading, independently of how far it projects into a locking channel. Consequently, it is not possible to deduce the location of the locking edges of the relevant tumbler by probing the displacement travels of the tumblers. The control gate of the flat key is equipped with control edges that displace the tumblers by a desired number of increments when the flat key is inserted into the passage formed by the key openings. The maximum displacement travel of the tumblers in this design is divided into uniform increments that are specified by the control gate. In particular, different codings for the lock cylinder can be implemented by the number of increments as well as by the number of tumblers.